Electrically heated window glazings



3,366,777 ELECTRICALLY HEATED WINDOW GLAZINGS Kenneth W. Brittan, 6 Lewis Crescent, Great Abindton, near Cambridge, Cambridgeshire, England, and David Hampson, 22 Foxland Ave., Retinal, Birmingham, England Continuation-impart of application Ser. No. 283,824, May 28, 1963. This application Jan. 16, 1967, Ser. No. 609,530

1 Claim. (Cl. 219-522) ABSTRACT OF THE DISCLOSURE TWO electrically insulating coatings sandwiching an electrically conductive film between them are used on a sheet of glass as a base. The insulating coatings are thick as compared to the film and the point of a heated rod is used to burn or melt through the outer coating and the film to but not through the inner coating. This allows the burn line to be very narrow which, together with the presence of the underlying coating, causes these lines to be barely perceptible.

This application is a continuation-in-part of our copending application Ser. No. 283,824, filed May 28, 1963, now abandoned.

. Brief summary of the invention This invention relates to transparent window glazings of a kind carrying a thin conducting film (of the order of 0.0000002 thinness) and bus bars in electrical contact with opposite edges of the film, said film being formed on an electrically insulating coating adhering to the glazing, the coating being of a thinness of the order of 0.000006, the film and coating being intimately adherent the one to the other.

A window glazing of the kind above referred to may consist of a single sheet of glass, for example that type of glass known as plate glass or float glass or may consist of a laminated assembly comprising sheets of glass between which sheets are interposed bonding layers, and the transparent electro-conductive film is formed on either one or both faces of the glazing. The film may be a gold film or may be a film made of tin oxide and the film is used so as to constitute an electric heating medium. Experience has shown that it is frequently necessary, on account of the voltage supply available, the size or shape of the base, and the limits of resistance to which the film can be formed with the desired degree of transparency, to increase the resistance of the film by dividing the film into separate areas, which areas are then electrically connected together by the bus bars.

Bus bars of greater conductivity than the film are conventionally formed on the transparent glazing along two opposed edges of the filmed area. If the voltage is high in relation to the resistance of the film, a non-conductive barrier or barriers is inserted in the film running from one bus bar to the other and one or both bus bars may be divided into sections so that, for example, the separate filmed areas are arranged electrically in series.

Alternatively, one bus bar may be divided into three sections and the film provided with barriers so that it is divided into three physically separate areas which can be supplied via the divided bus bar from a three-phase supply, the opposite bus bar being unbroken and forming the star point of the circuit.

Asa further alternative each bus bar may be divided into two unequal parts and the film divided by barriers into three areas supplied from the bus bars in delta connection.

3,366,777 Patented Jan. 30, 1968 In any case, the barriers are lines or intervals of discontinuity in the conductive film and although various techniques have been used and proposed to provide these discontinuities, they have been plagued with a common problem when the films are used to heat transparent materials such as the windscreen or canopy of an aircraft, for example. This problem has to do with the fact that with prior art arrangements, the discontinuities in the conductive film have been readily discernible so that their presence causes an annoying and potentially dangerous distraction.

According to the present invention, the problem is overcome by an arrangement which produces a twofold eifect resulting in lines of discontinuity which are barely perceptible. Specifically, the present invention embodies an electrically conductive film superimposed over a coating of electrically insulating material in which the coating is relatively thick as compared to the film. The discontinuities are formed by burning or melting through the very thin film to but not through the underlying coating. The presence of the underlying coating allows the interval to be very narrow and since such underlying coating is not completely penetrated its physical boundaries are not sharply delineated. These two factors in combination serve to produce the above noted eifect, that the intervals are barely discernible and constitute a negligible source of distraction under the conditions set forth.

It is a primary object of this invention to provide an improved electro-conductive film which is divided into separate areas by minute intervals of high resistivity which intervals are not readily apparent to the eye of an observer.

Accordingly the present invention provides a transparent window glazing carrying a transparent thin conducting film (of the order of 0.0000002" thinness) and bus bars in electrical contact with opposite edges of the film, said film being formed on an electrically insulating coating adhering to the glazing, the coating being of a thinness of the order of 0.000006", the film and coating being intimately adherent the one to the other, characterized in that the film is divided into electrically separate but adjacent areas in electrical connection with the bus bars by ruling an interval extending between the bus bars through the film to the coating, and constituted by the adjacent film edges exposed at the interval and the coating material below them, the film edges at the interval being less than of an inch apart, said interval constituting an electrical insulation between the adjacent film areas and being substantially invisible when observed in the light passing through the glazing.

More particularly, the present invention comprises a transparent window glazing carrying a transparent thin conducting film (of the order of 0.0000002" thinness) and bus bars in electrical contact with opposite edges of the film, said film being formed on an electrically insulating coating adhering to the glazing, the coating being of a thinness of the order of 0.000006", the film and coating being intimately adherent the one to the other, characterized in that the film is divided into electrically separate but adjacent areas in electrical connection with the bus bars by ruling an interval extending between the bus bars through the film to the coating under thermal conditions, ensuring a severance of the film restricted to the line of the interval, and constituted by the adjacent film edges exposed at the interval and the coating material below them, the film edges at the interval being less than A of an inch apart, said interval constituting an electrical insulation between the adjacent film areas and being invisible When observed in the light passing through the glazing.

It is found that narrow intervals, i.e. of less than one hundredth of an inch thickness which are free from the electro-conductive material are substantially invisible when observed in light passing through the transparent base, and are not sufficiently apparent to be a cause of distraction to an aircraft pilot.

Preferably the narrow intervals are less than 0.006" in width and advantageously are between 0.002 and 0.004" in width.

One embodiment of the invention is shown, by way of example, in the accompanying drawings, in which:

FIGURE 1 is a plan view of a glass base having thereon a transparent film which is divided into two areas by a narrow interval, and

FIGURE 2 is a greatly enlarged fragmentary sectional view of the glazing and transparent film of FIGURE 1 taken along the lines 2-2 of FIGURE 1.

Referring to FIG. 1, a Windscreen or similar assembly 10 is shown therein which comprises a base in the form of a sheet of glass 12 (FIG. 2) provided with a transparent layer, herein more particularly described, which is divided by an interval 14 into separate areas 16 and 18 which are electrically conductive. A common bus bar 20 along one edge of the windscreen is electrically connected to the electrically conductive portions of both areas 16 and 18 while separate bus bars 22 and 24 along the opposite edge of the windscreen are in contact with respective areas 16 and 18. The bus bars 22 and 24 are provided with suitable terminal portions 26 and 28 for connection to an external source of electrical potential so that the areas 16 and 18 are electrically connected in series.

The exact configuration of the windscreen, the location of the interval 14 and relative proportion of the areas 7 16 and 18 are of no significance insofar as the present invention is concerned. It will be recognized by those skilled in the art that these factors will depend upon the conditions encountered in a particular situation. A great many intervals could be provided with intervening areas of disparate cross-sectional widths and lengths, all in accord with conventional practice.

The invention herein concerns the arrangement shown in FIG. 2. In this figure, it will be apparent that the base 12 is first provided with an electrically insulating coating 30 on one face thereof. This coating preferably consists of bismuth oxide having a thickness of about 6X10 inches and may be applied by any conventional technique. Applied to and intimately adhered to this coating is a film 32 of gold having a thickness of about 2X10 inches and which may be applied by conventional .techniques such as sputtering or thermal evaporation. Lastly, an external or protective coating 34 of bismuth oxide is applied to the film 32, its thickness being about X10 inches.

The interval 14 is formed by engaging the tip or point of a heated rod against the surface of the external coating 34 and moving this point at a uniform rate across such surface. Preferably, the rod is tungsten having a diameter of A1" ground to a hemispherical point having a radius of about 0.005". The body of the rod is maintalned at a temperature of about 700 C. and is traversed at a rate of approximately one inch per second. This will produce an interval 14 substantially as shown in FIG. 2.

As shown, the external coating 34 is completely penetrated and removed along the line of the interval 14 as is the electrically conductive film 32. With the above specified conditions prevailing, the distance between the film edges 36 and 38 is approximately 0.003" and the trough or bottom 40 of the interval 14 penetrates only slightly into the underlying coating 30.

Since not all, but onlypart, of the total thickness of the several coatings is penetrated along the line of the interval, the boundaries of the interval are capable of variation as would not be the case were the total thickness completely penetrated. This is made possible only because of the underlying coating 30 of electrically insulating material since the conductive film 32 must be penetrated and ruptured in order to provide the electrical discontinuity. Thus the coating 30 serves to elevate the conductive film 32 above the glass surface so that it is accessible for penetration. Moreover, the width of the penetration line can be controlled within smaller limits because of its elevation above the glass surface and the possibility of selective variation of the depth of penetration into the coating 30. Lastly, the presence of the coating 30 protects the glass surface and eliminates the chance of damage thereto as might cause local weakness leading to failure.

The protective external layer 34 also plays a part in controlling the width of the line of penetration through the conductive film 32. By its presence, the rate of feeding the rod across its surface and the temperature of the rod are not so critical as would be the case if the external coating were to be eliminated. If the external coating 32 were eliminated, it will be apparent that it would be difiicult to obtain a narrow separation between the edges 36 and 38.

In any event, it is desirable that the depth of penetration be not much more than about 50% of the total thickness of the several coatings.

If the conductive film is of gold, the rod point is maintained at a temperature of about 400 C. to 900 C. Alternatively, however, the conductive film may be of tin oxide, when the point would be at a temperature of about 600 C. to 1200 C. In each case the temperature selected for the point will be related to the speed at which the point is moved across the surface of the glass or other transparent base, e.g. by the aid of a pantograph.

T-he transparent electro-conductive film is preferably of gold and may be applied to the selected form of glazing as a continuous whole by sputtering or by thermal evaporation to achieve a film of gold 0.0000002 thick on a substratum of bismuth oxide 0.000006" thick and with a protective coating of bismuth oxide 0.000005 thick. The narrow intervals of high resistivity are formed by ruling lines on the film with a heated point which point penetrates the film and severs it by burning it off or melting it along the lines of contact. The ruled lines may be straight or curved. The heated point may be formed from a A3" diameter tungsten rod, the point of which is ground to an approximately spherical shape of 0.005" radius. It may be heated by an insulated coil of Nichrome wire to a temperature of about 700 C. and is traversed across the film at approximately one inch per second. It will be understood that the temperature of the main body of the point or rod is about 700 C., but the temperature of the extreme tip of the point or rod is somewhat lower, probably of the order of 400 C.

By the use of this invention, there is obtained a transparent glazing with an electro-conductive film having one or more highly resistive or substantially non-conductive intervals of very small width of the order of 0.006" or less which by reason of their width are not readily visible and therefore do not form a source of distraction. Furthermore the preferred method according to the invention provides means for producing such intervals without risk of damage to the adjacent films or to the surface of the glass or other transparent base.

What is claimed:

1. In a transparent window glazing,

spaced bus bars attached to opposite edges of said glazing and adapted to be connected to a source of electrical potential,

an inner transparent coating of electrically insulating material extending in continuous and uninterrupted fashion in the region between said bus bars,

a transparent film of electrically conductive material adherently contacted upon said inner coating, said film being divided into at least two areas, electrically connected by said bus bars with adjacent side edges of such areas being in closely spaced relation,

said side edges being spaced apart not more than about 0.01.

said inner coating being at least about 30 times the thickness of said film, and

an external transparent coating of electrically insulating material covering said areas of the film.

References Cited UNITED STATES PATENTS 6 Cowdrey et al. 219543 X 'Egle et al. 219-345 Thomson et al 338292 Gaiser 219-522 X Ryan et a1 219-203 X Griest el al. 338-309 RICHARD M. WOOD, Primary Examiner.

10 V. Y. MAYEWSKY, Assistant Examiner. 

